how to compare two objects for equality if they have functions? lodash's isEqual works really well until functions are thrown in:

_.isEqual({
    a: 1,
    b: 2
}, {
    b: 2,    
    a: 1
});

// -> true

_.isEqual({
    a: 1,
    b: 2,
    c: function () {
        return 1;
    }
}, {
    a: 1,    
    b: 2,
    c: function () {
          return 1;
    }
});

// -> false

how to compare two objects for equality if they have functions? lodash's isEqual works really well until functions are thrown in:

_.isEqual({
    a: 1,
    b: 2
}, {
    b: 2,    
    a: 1
});

// -> true

_.isEqual({
    a: 1,
    b: 2,
    c: function () {
        return 1;
    }
}, {
    a: 1,    
    b: 2,
    c: function () {
          return 1;
    }
});

// -> false

• javascript
• lodash

• two anonymous function have two different prototypes, so two different objects! – user757095 Commented May 13, 2015 at 10:37
• It really depends on what you are going to compare. Best solution would be to create a hash unique per object and compare it, or, knowing the structure, make an equal function for that particular object. – Jack Commented May 13, 2015 at 10:40
• Even though the functions do the same, they will never be equal. Do you want to ignore the functions and compare? – thefourtheye Commented May 13, 2015 at 10:54

4 Answers 4

Are you sure you want to compare functions? If you only care about comparing every property that isn't a function, this is easy to do with lodash:

var o1 = { a: 1, b: 2, c: function() { return 1; } },
    o2 = { a: 1, b: 2, c: function() { return 1; } };

_.isEqual(o1, o2)
// → false

_.isEqual(_.omit(o1, _.functions(o1)), _.omit(o2, _.functions(o2)));
// → true

The functions() function returns a list of function properties, and using omit(), you can get rid of them.

This is what I tried:

_.isEqual(o1, o2, function(val1, val2) {
  if(_.isFunction(val1) && _.isFunction(val2)) {
    return val1.toString() === val2.toString();
  }
})

Lodash supports a customizer function which allows you to write your own equality checks. This seems to be a good enough test to see if the functions are character by character the same.

Try isEqualWith instead:

import { isEqualWith, isFunction } from 'lodash-es'

const o1 = { fn() {} }

const o2 = { fn() {} }

const equal = isEqualWith(o1, o2, (v1, v2) =>
  // if `customizer` returns `undefined`, comparisons are handled by the method instead
  isFunction(v1) && isFunction(v2) ? `${v1}` === `${v2}` : undefined,
)

console.log({ equal }) // { equal: true }

As the lodash documentation states:

Functions and DOM nodes are not supported.

https://lodash.com/docs#isEqual